Finneran James J, Schlundt Carolyn E
U.S. Navy Marine Mammal Program, Space and Naval Warfare Systems Center, San Diego, Code 2351, San Diego, California 92152, USA.
J Acoust Soc Am. 2007 Jul;122(1):606-14. doi: 10.1121/1.2743158.
Studies of underwater hearing are often hampered by the behavior of sound waves in small experimental tanks. At lower frequencies, tank dimensions are often not sufficient for free field conditions, resulting in large spatial variations of sound pressure. These effects may be mitigated somewhat by increasing the frequency bandwidth of the sound stimulus, so effects of multipath interference average out over many frequencies. In this study, acoustic fields and bottlenose dolphin (Tursiops truncatus) hearing thresholds were compared for pure tone and frequency modulated signals. Experiments were conducted in a vinyl-walled, seawater-filled pool approximately 3.7 x 6 x 1.5 m. Acoustic signals were pure tone and linear and sinusoidal frequency modulated tones with bandwidths/modulation depths of 1%, 2%, 5%, 10%, and 20%. Thirteen center frequencies were tested between 1 and 100 kHz. Acoustic fields were measured (without the dolphin present) at three water depths over a 60 x 65 cm grid with a 5-cm spacing. Hearing thresholds were measured using a behavioral response paradigm and up/down staircase technique. The use of FM signals significantly improved the sound field without substantially affecting the measured hearing thresholds.
水下听力研究常常受到小型实验水箱中声波行为的阻碍。在较低频率下，水箱尺寸往往不足以满足自由场条件，导致声压出现较大的空间变化。通过增加声音刺激的频率带宽，这些影响可能会有所减轻，这样多径干扰的影响会在许多频率上平均化。在本研究中，对纯音和调频信号的声场及宽吻海豚（宽吻海豚）听力阈值进行了比较。实验在一个约3.7×6×1.5米的乙烯基壁、充满海水的水池中进行。声学信号为纯音以及带宽/调制深度为1%、2%、5%、10%和20%的线性和正弦调频音。在1至100千赫之间测试了13个中心频率。在一个60×65厘米的网格上，间隔5厘米，在三个水深测量了（海豚不在场时的）声场。使用行为反应范式和上下阶梯技术测量听力阈值。使用调频信号显著改善了声场，而对测得的听力阈值没有实质性影响。
